Blackout Leaves Southwest in the Dark

11/01/2011 | Sonal Patel

A large swath of Southern California, parts of Arizona, and Northern Baja Mexico was blacked out on Sept. 8—leaving seven million people in the dark—after an Arizona utility worker fixing faulty equipment near Yuma reportedly tripped the 500-kV North Gila–Imperial Valley transmission line, causing the outage. The blackout prompted two units at the San Onofre Nuclear Generating Station to go offline, stranded many people in elevators and trains, shut down airports, cut air conditioning on a day well above 90F, and caused damages of $97 million to $118 million, according to early estimates from the National University System’s Institute for Policy Research.

The San Diego blackout, as it is being called—which lasted 15 hours in some parts of the Southwest (Figure 1)—is the most severe interstate incident since the massive outage that knocked out power for much of the U.S. Northeast in 2003.

1. Strangely dark San Diego. A large swath of Southern California, Arizona, and Northern Baja Mexico experienced a blackout—15 hours long in some areas—reportedly caused by 23 events on five different grids over an 11-minute stretch on the afternoon of Sept. 8. Courtesy: Victoria Freeman

The cause has not been firmly established, but Phoenix-based Arizona Public Service Co. said that it was related to a procedure an employee was carrying out in the North Gila substation, located northeast of Yuma, at about 3 p.m. “Operating and protection protocols typically would have isolated the resulting outage to the Yuma area. The reason that did not occur in this case will be the focal point of the investigation into the event, which already is underway,” the utility said.

Seconds after the worker shorted out the high-voltage power line, one of three turbines generating power at a plant east of Mexicali shut down, creating an imbalance in the line running south from the San Onofre plant, Stephen Berberich, CEO of the California Independent System Operator (ISO) told the San Diego Union-Tribune days after the blackout. The situation was worsened by 22 other events on five different grids over an 11-minute stretch that culminated in the massive blackout, he said.

Investigations into the blackout are ongoing. The Federal Energy Regulatory Commission (FERC) and the North American Electric Reliability Corp. (NERC) announced a joint inquiry into the Sept. 8 outage. FERC and NERC said they would coordinate with the Department of Energy and other federal agencies, the California ISO, the Western Electricity Coordinating Council, California and Arizona state regulators, and the companies involved to monitor the situation. The inquiry will focus on causes of the incident.

—Sonal Patel is POWER’s senior writer.

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